What Factors Should be Considered When Choosing the Right 400G Transceiver for Multimode Fiber? What are the Most Common Applications for Each Transceiver Type?

Selecting the right 400G transceiver for multimode fiber involves many factors. Here are some of the key considerations:

Distance: The range of operations for each type of transceiver varies. Before choosing a transceiver, you should know the exact distance between the systems you plan to connect. Short-range transceivers are typically used for distances up to 70m, while long-range variants can cover distances above 2km.

Power Consumption: Power usage can vary substantially from one transceiver type to another.  Higher capacity transceivers often use more power. Ideally, you should aim for a transceiver that offers the required data rate at the lowest possible power consumption.

Cost: Pricing can vary significantly between different transceivers. The overall cost should be evaluated in the context of your specific networking needs and budgetary constraints.

Compatibility: Not all transceivers will be compatible with your switches, routers, or other network devices. Be sure to confirm that the transceiver you choose works with your existing hardware.

Interconnection: Consider how different transceivers suit your interconnection environments. Transceivers come in different form factors such as QSFP-DD, OSFP, CFP2, CFP8, or COBO, and each has its own specifications for things like power consumption, size, and interface.

Reliability and Durability: The lifespan and durability of the transceivers also come into play. High-quality transceivers are built to last, reducing the need for replacements and maintenance.

The key features and common applications of each of these transceivers are described below.

1.The OSFP-400G-SR8 / SR8-C and QDD-400G-SR8 / SR8-C

The 400G-SR8 was the first 400G MMF transceiver available and has been deployed for point-to-point 400GE applications, such as leaf-to-spine connectivity, illustrated below.

While the 400G-SR8 provides cost-effective 400GE connectivity over MMF, it requires 16 fibers per transceiver and uses an MPO-16 APC fiber connector. Most 40G and 100G parallel MMF optics (such as the 40G-SR4 and 100G-SR4) use MPO-12 UPC fiber connectors. MPO-16 to 2x MPO-12 patch cables are required to use a 400G-SR8/SR8-C transceiver over an MPO-12 UPC-based fiber plant.

Another key application for 400G-SR8 transceivers is optical breakout into 2x 200G-SR4 links, enabling TOR-to-host connectivity where 200G to the host is required, as illustrated below.

The 400G-SR8-C transceiver has the same features as the 400G-SR8, with the added ability to breakout into 8x 50G-SR or 8x 25G-SR optical links. It can therefore be used in applications that require high-density 50G or 25G breakouts – as illustrated below.

2. The OSFP-400G-SRBD and QDD-400G-SRBD, or “400G-BIDI”transceivers.

400G-BIDI transceivers use the widely deployed MPO-12 UPC connector for parallel multimode fiber. This allows existing 40G or 100G links that use 40G-SR4 or 100G-SR4 QSFP optics to be upgraded to 400GE with no change to the fiber plant, as illustrated below:

When configured for 400GE operation, the 400G-BIDI transceiver is compliant with the IEEE 400GBASESR4.2 specification for 400GE over 4 pairs of MMF.

Arista’s 400G-BIDI transceivers are also capable of breaking out into 4x 100GE links and can be configured (via EOS) to interoperate either with the widely deployed base of 100G-BIDI (100G-SRBD) transceivers, or newer 100G-SR1.2 transceivers, as indicated below.

In summary, Arista’s 400G-BIDI transceiver is software configurable to operate in any one of three operating modes:

i) 400G-SR4.2 for point-to-point 400GE links

ii) 4x 100G-BIDI for breakout and interop with 4x 100G-BIDI (100G-SRBD) transceivers

iii) 4x 100G-SR1.2 for breakout and interop with 4x 100G-SR1.2 transceivers